When conduits, such as gas pipelines, are installed underwater they often can not lie flat on the ocean floor. Rather, depressions or risers on the ocean floor may result in unsupported pipeline spans of considerable length. Some means must be provided to support the pipeline at such locations in order to prevent dynamic vortex-induced oscillations of the pipeline and subsequent risk of fatigue failure. For gas pipelines, the risk of stress fatigue is particularly acute when the pipeline is initially hydrotested.
Conventionally, cement grout is pumped from a surface vessel into bags placed underneath the pipeline span which is to be supported. This is an extremely costly and time-consuming procedure, especially in areas having undulating terrain. If the seabed slope is particularly steep or the soil soft, special care must be taken to prevent the grout support bags from slipping out of place before the grout has set. In such instances grout bags must be filled gradually via several successive pours of grout material. Even if precautions are taken, failure rates on the order of 50% may occur.
The time required to position and fill a single, multi-layered grout bag in deep water is typically on the order of 24-36 hours. Installation time may be lengthened significantly in the event of inclement weather, since the surface vessel must be maintained in a relatively stationary position during the entire procedure. Another major drawback of the conventional procedure is that a large amount of equipment and manpower is required to position and fill the grout bags.
It is known in the prior art to provide mechanical devices for engaging and elevating conduits, such as lengths of drill pipe and the like. For example, U.S. Pat. No. 4,511,169, which issued to Willis on Apr. 16, 1985, discloses a self-locking and unlocking elevator assembly which includes a pair of jaws having clamping surfaces for automatically engaging a tubular length of drill pipe as the elevator assembly is lowered into place over the pipe. U.S. Pat. No. 4,522,439, which issued to Haney on Jun. 11, 1985, also discloses an elevator assembly having jaws to allow closure over and clamping of a length of pipe.
However, the Willis and Hayne devices referred to above are primarily designed for successively removing lengths of drill pipe from a vertical bore hole and are not adapted for supporting selected portions of a gas pipeline laid over irregular seabeds. Accordingly, the need has arisen for a clamping apparatus which may be lowered onto a length of conduit from above and which includes means for automatically engaging the conduit and for securely anchoring the conduit above a support surface, such as the ocean floor.